Please help: 97% CPU cycles are wasted in disk I/O wait on FC4/FC5?
Robinson Tiemuqinke
hahaha_30k at yahoo.com
Sat May 6 07:07:28 UTC 2006
Hi,
Just found a strange things happened on my FC4/FC5
boxes: around 90% CPU times are wasted in disk I/O
wait when I doing a simple "dd if=/dev/sdb
of=/dev/null >/dev/null 2>&1 &" test. vmstat shows the
CPU cycles when there are I/O waiting. And at these
times ssh sessions and keyboard response is pretty
slow.
On old FC1 and Redhat 9 I did't see this problem, I
configured 2.4 kernels to accept other Interrupts
during disk I/O to for much beter interactive
responses. How can I do it again on 2.6 kernels?
The following is my test results. Please have a look
and help.
[root at testnode01 ~]# vmstat 2 100
procs -----------memory---------- ---swap--
-----io---- --system-- ----cpu----
r b swpd free buff cache si so bi
bo in cs us sy id wa
1 0 160 29792 2626332 556320 0 0 1849
18 695 148 1 1 96 2
0 0 160 29304 2626368 556284 0 0 110
42 286 47 14 0 83 3
0 0 160 34880 2626396 550100 0 0 156
44 289 68 9 2 84 5
[root at testnode01 ~]# dd if=/dev/sdc of=/dev/null 2>&1
&
[1] 9933
[root at testnode01 ~]# vmstat 2 100
procs -----------memory---------- ---swap--
-----io---- --system-- ----cpu----
r b swpd free buff cache si so bi
bo in cs us sy id wa
1 2 160 20284 2747752 441056 0 0 1853
18 694 148 1 1 96 2
0 1 160 20496 2865276 321480 0 0 59062
0 499 530 11 13 0 77
0 1 160 20604 2981924 202780 0 0 58496
46 493 518 4 13 0 83
0 1 160 20508 3099396 83256 0 0 59008
24 499 528 3 14 0 83
0 1 160 21372 3156688 23912 0 0 59008
0 497 519 4 13 0 83
[root at testnode01 ~]# cat /proc/loadavg
0.51 0.23 0.10 2/84 9937
[root at testnode01 ~]# uname -a
Linux testnode01.example.com 2.6.15.6_64_v3tcp #1 SMP
Fri Mar 17 16:59:19 PST 2006 x86_64 x86_64 x86_64
GNU/Linux
[root at testnode01 ~]# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 3
model name : Intel(R) Pentium(R) 4
CPU 3.60GHz
stepping : 4
cpu MHz : 3600.302
cache size : 1024 KB
fpu : yes
fpu_exception : yes
cpuid level : 5
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8
apic sep mtrr pge mca cmov pat pse36 clflush dts acpi
mmx fxsr sse sse2 ss ht tm syscall lm constant_tsc pni
monitor ds_cpl cid xtpr
bogomips : 7211.15
clflush size : 64
cache_alignment : 128
address sizes : 36 bits physical, 48 bits virtual
power management:
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